<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    img {
      width: 100%;
      height: 100%;
      display: block;
    }

    .box {
      width: 450px;

      margin: 50px;
      display: flex;
      flex-direction: column;

      position: relative;
    }

    .box>.show {
      width: 450px;
      height: 450px;
      border: 1px solid #333;
      position: relative;
    }

    .box>.show>.mask {
      width: 200px;
      height: 200px;
      background-color: yellow;
      opacity: .4;
      position: absolute;
      top: 0px;
      left: 0px;

      display: none;
    }

    .box>.list {
      width: 100%;
      flex: 1;

      display: flex;
      justify-content: flex-start;
      align-items: center;

      box-sizing: border-box;
      padding: 20px;
    }

    .box>.list>p {
      width: 54px;
      height: 54px;
      border: 1px solid #333;
      margin-right: 10px;
    }

    .box>.list>p.active {
      border-color: red;
    }

    .box>.enlarge {
      width: 400px;
      height: 400px;

      position: absolute;
      top: 0;
      left: 101%;

      background: url(./imgs/1.big.jpg) no-repeat;
      background-size: 800px 800px;
      background-position: 0 0;

      display: none;
    }
  </style>
</head>

<body>

  <div class="box">
    <div class="show">
      <img src="./imgs/1.jpg" alt="">
      <div class="mask"></div>
    </div>
    <div class="list">
      <p class="active">
        <img src="./imgs/1.small.jpg" showImg="./imgs/1.jpg" enlargeImg="./imgs/1.big.jpg" alt="">
      </p>
      <p>
        <img src="./imgs/2.small.jpg" showImg="./imgs/2.jpg" enlargeImg="./imgs/2.big.jpg" alt="">
      </p>
    </div>
    <div class="enlarge"></div>
  </div>
  <script>
    /* 
    分析需求：1、鼠标移入 遮罩层和 放大图都需要显示，鼠标移除的时候 遮罩层和放大图隐藏
            2、鼠标在移动的时候遮罩层要跟着鼠标动 （鼠标的中间动）（边界问题）
            3、放大图也要按照左边比例来移动
            4、鼠标移到小图上可以切换图片
     */
    let showin = document.querySelector(".show")
    let maskin = document.querySelector(".mask")
    let enlargein = document.querySelector(".enlarge")
    let picture = document.querySelectorAll(".list p")
    let imgin = document.querySelector(".show img")
    let boxin = document.querySelector(".box")
    showin.onmouseenter = function () {
      maskin.style.display = "block"
      enlargein.style.display = "block"
    }
    showin.onmouseleave = function () {
      maskin.style.display = "none"
      enlargein.style.display = "none"
    }
    showin.onmousemove = function (e) {
      let x = e.clientX - maskin.offsetWidth / 2 - boxin.offsetLeft
      let y = e.clientY - maskin.offsetHeight / 2 - boxin.offsetTop
      if (x < 0) {
        x = 0
      } else if (x > showin.offsetWidth - maskin.offsetWidth) {
        x = showin.offsetWidth - maskin.offsetWidth
      } else if (y < 0) {
        y = 0
      } else if (y > showin.offsetHeight - maskin.offsetHeight) {
        y = showin.offsetHeight - maskin.offsetHeight
      }
      maskin.style.top = y + "px"
      maskin.style.left = x + "px"
    }
  </script>


</body>

</html>